In large multiple fuel tank installations, for example on petrol station forecourts, there may be a number of storage tanks intended for different grades or types of fuel. Unintentional contamination of one fuel by another, can easily take place if care is not taken when the fuels are delivered and, can cause considerable damage, for example if diesel fuel finds its way into a petrol tank, or vice versa. Since all of these fuels are commonly delivered by tankers with multiple fuel compartments, and all of the storage tanks have similar filler inlets, such an error can easily occur if the tanker operative is in a hurry.
International patent application no. WO 00/55598 (Masstech International Limited) describes a device for detecting the presence of a chemical contaminant, the device comprising an indicator element which is held in a first position by means of a failure element which is held in tension, the failure element being made of a material which fails in the presence of the chemical to be detected, thereby releasing the indicator element from its first position and allowing it to move into a second position in order to provide an indication of the presence of the contaminant.
The failure of the failure element may occur by shearing or stretching of the element, or, more typically, may occur when the surface of the element is degraded by the contaminant, in such a way as to release it from engagement with another part of the mechanism.